Age-related hearing loss (ARHL) is an epidemic influencing the lives of 48 million Americans6. Current clinical protocols to detect ARHL leave room for much improvement so that early diagnosis and intervention can be achieved. One way to improve current clinical protocols is through the implementation of fast, objective, and sensitive tests of cochlear function using tools such as stimulus frequency otoacoustic emissions (SFOAEs). SFOAEs are currently not utilized clinically, despite their potential for assessing the cochlea in a frequency- specific manner19-24 and sensitivity to minor insults to the cochlea25,26. Before clinical implementation of SFOAEs can be pursued, three major gaps in knowledge must be addressed. First, the relationship between SFOAEs and psychophysical measures of hearing must be thoroughly examined across the entire range of human hearing. Second, the sensitivity of SFOAEs must be evaluated for detecting cochlear changes due to developmental and aging processes. Third, using SFOAEs, cochlear contributions in functionally relevant auditory deficits must be determined. Recent findings suggest that SFOAEs may be more sensitive than behavioral thresholds to age-related cochlear changes25. However, a deeper examination is needed to determine how SFOAEs are influenced during a critical period of human life, which shows early aging effects in distortion product OAEs38. In evaluating the potential of SFOAEs in the accurate and early detection of cochlear dysfunction due to ARHL, the specific aims of this proposal are to investigate the relationship between SFOAEs and psychophysical measures of hearing up to the highest measurable frequency (Aim 1), to examine the developmental and aging effects of OHC function using SFOAE amplitudes and phase slopes (Aim 2) and to apply this understanding to validate the clinical utility of SFOAEs in detecting OHC contributions to speech perception in noise (SPIN) deficits (Aim 3). In Aim 1, the relationship between thresholds derived from SFOAE input-output functions with those obtained behaviorally will be evaluated. Additionally, tuning estimates derived from SFOAE phase slopes will be compared to psychophysical tuning curves. In Aim 2, a cross-sectional investigation of cochlear function across a significant portion of human lifespan (7 - 45 years) will be performed using both behavioral thresholds and SFOAE amplitudes and phase spanning a significant range of human hearing (0.5 - 20 kHz) using state- of-the-art calibration techniques68-74. In Aim 3, SFOAEs as well as neural measures will be examined in individuals with SPIN deficits. By addressing the aims of this proposal, the long-term objective to advance the clinical applicability of SFOAEs for detecting age-related cochlear dysfunction can be pursued.